add databse

displaced previously used text files with a sqlite database
raw.db     -->  alldata.txt feature.txt param.txt 
train.db   -->  trainset.txt
test.db    -->  testtest.txt
therefore, prepare.py has been thoroughly substituted.
in raw data, directory like htc which contains data files of specific device has been moved to a raw_data/devices

other files has been modified in varying degrees in order to adapt to the new structure of database.(including:offline.sh, online.sh, server.py, files in alg)

added dbhelper.py for the convenience of database manipulation.

added util.py for common methods in the future. currently, we have a function for fetching host ip address 

added go.sh to take the role of offline.sh and online.sh, now users can run offline phase and online phase by only one command

removed gen_tset.py and test_set_mz.txt in test

removed predicor.py in script